It is known in the art to utilize heatsinks for dissipating heat generated by electronic circuits in modern devices. Such well known heatsinks typically comprise a base unit to which the heat generating electronic devices are mounted, and a plurality of fins projecting from the base unit for dissipating the generated heat. It is an object of these heatsinks to maximize the surface area of the fins in order to provide optimum heat transfer from the heat sink to the surrounding atmosphere. It is a further object of well known heatsinks to provide a good thermal contact between the base unit and the fins.
In order to achieve the latter mentioned object, according to known prior art methods, heatsinks have been fabricated by metal extrusion through a die which is cut to the required shape specifications such that the base unit and fins are of integral construction. However, as discussed above, efficiency of operation of such heatsinks is regulated by the surface area and amount of metal used versus the length of each fin. The current design limit for prior art extrusion processes in terms of fin thickness to height, is 3:1 or less. Thus, in the event that, an extruded fin is excessively thin or excessively high, the pressure of the extruded metal has a tendency to destroy the die.
In an effort to overcome the problems of integral extruded heatsinks, and in an effort to provide increased fin density and overall height, certain prior art fabrication methods have used separate extrusion of the base unit and the fins, and subsequent assembly to form the heatsink. For example, U.S. Pat. No. 3,261,396 (Trunk) teaches a method of securing corrugated metal fins to a base unit by means of epoxy cement. Unfortunately, the epoxy gluing method disclosed in the Trunk patent results in poor thermal conductivity between the base unit and respective fins.
U.S. Pat. No. 3,216,496 (Katz) teaches separate fabrication of a bus bar or base unit having, on its flat side, a plurality of slots for receiving separately fabricated fins. The slots extend transversely the length of the bar and are arranged so as to hold the fins in substantially parallel relationship. The fins themselves are strip-shaped and preferably of width equal to that of the bus bar. The fins are joined to the bus bar by means of inserting the fins into the plurality of slots and then swaging the material between adjoining slots into intimate contact with the fins by means of a hydraulic press operating through a knife-edged tool. Unfortunately, the method taught by Katz applies pressure only to the narrow line contacted by the knife-edged tool. This results in the material of the bus bar being pushed to the side of the respective fins which creates an upward pressure tending to lift the fins upwardly from the grooves, thereby leaving an air space at the bottom of the grooves in the bus bar, which allows for air and moisture to enter resulting in corrosion and reducing the thermal contact between the base unit and fins.
Various other patents disclose methods of joining fins to a base unit. For example, U.S. Pat. Nos. 3,312,277 (Chitouras) and 3,280,907 (Hoffman) teach the use of dovetail connections for overcoming extrusion difficulties in fabricating a heat dissipating device with the fins very close together. Additional patents of interest are as follows: U.S. Pat. Nos. 941,375 (Loud et al); 2,639,119 (Greenwald); 2,944,326 (Stradthaus et al); 3,077,928 (Nihlen et al); and 4,733,453 (Jacoby). However, none of the above references teach effective means for overcoming the problem inherent in the Katz fabrication method by which the material of the base unit is pushed upwardly between respective ones of the fins thereby causing the fins to lift upwardly from the grooves.